Spiral assembly tool

ABSTRACT

An assembly tool for assembly of a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty. The tool includes a first member operably associated with the first component and a second member operably associated with the second component. The second member includes a cap having a threaded recess and further includes a threaded rod adapted to engage the threaded recess so as to move the second member relative to the first member and the threaded rod is made of a harder metal than the threaded recess.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of and claims priority to U.S. patent Ser. No. 12/815915 of the same title and filed on Jun. 15, 2010, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates generally to the field of orthopaedics, and more particularly, to an implant for use in arthroplasty.

BACKGROUND

Patients who suffer from the pain and immobility caused by osteoarthritis and rheumatoid arthritis have an option of joint replacement surgery. Joint replacement surgery is quite common and enables many individuals to function properly when it would not be otherwise possible to do so. Artificial joints are usually comprised of metal, ceramic and/or plastic components that are fixed to existing bone.

Such joint replacement surgery is otherwise known as joint arthroplasty. Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged joint is replaced with a prosthetic joint. In a typical total joint arthroplasty, the ends or distal portions of the bones adjacent to the joint are resected or a portion of the distal part of the bone is removed and the artificial joint is secured thereto.

Many designs and methods for manufacturing implantable articles, such as bone prostheses, are known. Such bone prostheses include components of artificial joints such as elbows, hips, knees and shoulders.

During performance of a joint replacement procedure, it is generally necessary to provide the surgeon with a certain degree of flexibility in the selection of a prosthesis. In particular, the anatomy of the bone into which the prosthesis is to be implanted may vary somewhat from patient to patient. Such variations may be due to, for example, the patient's age, size and gender. For example, in the case of a femoral prosthesis, the patient's femur may be relatively long or relatively short thereby requiring use of a femoral prosthesis which includes a stem that is relatively long or short, respectively. Moreover, in certain cases, such as when use of a relatively long stem length is required, the stem must also be bowed in order to conform to the anatomy of the patient's femoral canal.

Such a need for prostheses of varying shapes and sizes thus creates a number of problems in regard to the use of a one-piece prosthesis. For example, a hospital or surgery center must maintain a relatively large inventory of prostheses in order to have the requisite mix of prostheses needed for certain situations, such as trauma situations and revision surgery. Moreover, since the bow of the stem must conform to the bow of the intramedullary canal of the patient's femur, rotational positioning of the upper portion of the prosthesis is limited, thereby rendering precise location of the upper portion and hence the head of the prosthesis very difficult. In addition, since corresponding bones of the left and right side of a patient's anatomy (e.g. left and right femur) may bow in opposite directions, it is necessary to provide (left) and (right) variations of the prosthesis in order to provide anteversion of the bone stem, thereby further increasing the inventory of prostheses which must be maintained.

As a result of these and other drawbacks, a number of modular prostheses have been designed. As its name implies, a modular prosthesis is constructed in modular form so that the individual elements or figures of the prosthesis can be selected to fit the needs of a given patient's anatomy. For example, modular prostheses have been designed which include a proximal neck component which can be assembled to any one of numerous distal stem components in order to create an assembly which fits the needs of a given patient's anatomy. Such a design allows the distal stem component to be selected and thereafter implanted in the patient's bone in a position which conforms to the patient's anatomy while also allowing for a limited degree of independent positioning of the proximal neck component relative to the patient's pelvis.

One issue that arises as a result of the use of a modular prosthesis is the locking of the components relative to one another. In particular, firm, reproducible, locking of the proximal neck component to the distal stem component is critical to prevent separation of the two components subsequent to implantation thereof into the patient. The need for the firm locking is particularly necessary if the design does not provide for positive locking with weight bearing. As such, a number of locking mechanisms have heretofore been designed to lock the components of a modular prosthesis to one another. For example, a number of modular prostheses have heretofore been designed to include a distal stem component which has an upwardly extending post which is received into a bore defined distal neck component. A relatively long fastener such as a screw or bolt is utilized to secure the post with the bore. Other methods of securing modular components include the impacting of one component onto the other. This method has highly variable results.

Current designs of modular stems include designs in which the modular connection utilizes a tapered fit between the two components. For example, the proximal body may include an internal taper which mates with an external taper on the distal stem. Such a taper connection may be used in conjunction with additional securing means, for example, a threaded connection or may be used alone. It is important that the tapered connection be secure. For example, the proper amount of force must be applied to the tapered connection to properly secure the tapered connection so that the connection can withstand the forces associated with the operation of the stem.

Current attempts to provide a device to adjoin components of a modular joint prosthesis are fraught with several problems. For example, the device may not provide sufficient mechanical advantage to securely lock the components. Further, the ergonomics available to lock the components may not be optimal. There is thus a need to provide for an assembly tool capable of alleviating at least some of the aforementioned problems.

SUMMARY

According to one embodiment of the present invention, an assembly tool for assembly of a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty is provided. The tool includes a first member operably associated with the first component. The first member defines a first member longitudinal axis thereof. A second member is operably associated with the second component, and the second member defines a second member longitudinal axis thereof. A washer system is also included and is coupled to the second member. A drive mechanism is coupled to washer system, such that as the drive mechanism is activated, the washer system rotates about the second member longitudinal axis and expands along the second member longitudinal axis, wherein such movement further causes the second member to move relative to the first member along the second member longitudinal axis.

According to another embodiment of the present invention, a method for assembling a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty is provided. The method includes using an assembly tool having a first member and a second member. The second member defines a second member longitudinal axis. The assembly tool also includes a washer system coupled to the second member and a drive mechanism coupled to the washer system. The first component of the prosthesis is inserted onto the second component of the prosthesis. The second member of the assembly tool is secured onto the second component of the prosthesis. The drive mechanism is activated, causing the second member to move relative to the first member along the second member longitudinal axis.

According to yet another embodiment of the present invention, an assembly tool for assembly of a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty is provided. The tool includes a first member operably associated with the first component. The first member defines a first member longitudinal axis thereof. A second member is operably associated with the second component. The second member defines a second member longitudinal axis thereof, and the second member includes a tensile rod. A drive mechanism is coupled to the second member, such that as the drive mechanism is activated and reaches a predetermined load, the tension member breaks.

According to yet another embodiment of the invention, an assembly tool for assembly of a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty is provided. The tool includes a first member operably associated with the first component and a second member operably associated with the second component. The second member includes a cap having a threaded recess and further includes a threaded rod adapted to engage the threaded recess so as to move the second member relative to the first member and the threaded rod is made of a harder metal than the threaded recess.

According to another embodiment of the present invention, an assembly tool for assembly of a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty is provided. The tool includes a first member operably associated with the first component. The first member defines a first member longitudinal axis thereof. The tool further includes a second member operably associated with the second component. The second member includes a tensile bar adapted to break at a predetermined force, and the second member includes a housing adapted to retain the tensile bar after the tensile bar breaks.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in connection with the accompanying drawings.

FIG. 1 is a see-through perspective view of an assembly tool according to one embodiment of the present invention.

FIG. 2 is see-through view of the assembly tool of FIG. 1 coupled to a modular implant.

FIG. 3 is an enlarged see-through view of FIG. 2.

FIG. 4 is a perspective view of the assembly tool according to one embodiment of the present invention.

FIG. 5 is a perspective view of the washer assembly of FIG. 1.

FIG. 6 is a perspective view of the washer assembly of FIG. 5 in a rotated position.

FIG. 7 is a cut-away view of a tensile rod assembly of the assembly tool of FIG. 1.

FIG. 7 a is a close-up view of a washer system and a pull rod according to one embodiment of the present invention.

FIG. 8 is a flow chart of the method for using the assembly tool according to one embodiment of the present invention.

FIG. 9 is a partial see-through perspective view of an assembly tool according to one embodiment of the present invention.

FIG. 10 is another perspective view of the assembly tool of FIG. 9.

FIG. 11 is a partially exploded view of the assembly tool of FIG. 9.

FIG. 11 a is a close-up view of a portion of the assembly tool of FIG. 11.

FIG. 12 is a cut-away view of a first member of the assembly tool of FIG. 9.

FIG. 13 is a perspective view of a tensile bar and housing of the assembly tool of FIG. 9.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention and the advantages thereof are best understood by referring to the following descriptions and drawings, wherein like numerals are used for like and corresponding parts of the drawings.

FIG. 1 is a perspective view of an assembly tool 10 according to one embodiment of the present invention. The assembly tool 10 includes a first member 12 and a second member 14. Coupled to the second member 14 is a washer system 16. A drive mechanism 18 is coupled to the washer system 16. The first member 12 has a first member longitudinal axis 20 and the second member 14 has a second member longitudinal axis 22. In the illustrated embodiment, the first member longitudinal axis 20 and the second member longitudinal axis 22 are co-incident. In other embodiments, the two axes 20, 22 may be parallel or offset at an angle from one another. As the drive mechanism 18 is activated, it causes the washer system 16 to rotate about the second member longitudinal axis 22. In the illustrated embodiment, the drive mechanism is a handle that is ratcheted about the second member longitudinal axis 22. However, in other embodiments, it could be a longitudinal handle, a Hudson connection that connects to a power source, or other known drive mechanism that would cause the washer system 16 to rotate about the second member longitudinal axis 22.

Referring now to FIG. 2, a see-through view of the assembly tool 10 is shown coupled to a modular implant 23. As shown, the modular implant 23 includes a first component 24 (or a proximal or neck component) and a second component 26 (or a distal or stem component). The first member 12 of the assembly tool 10 includes a distal end 28 that abuts a proximal end 30 of the neck component 24. In other embodiments, other connection means may be used. For example, the distal end 28 may include threads that engage a threaded end of the proximal end 30 of the neck component 24. Alternatively, the connection means may be a retractable button/recess system, a slotted l-shaped recess and rod system, an undercut, an expandable collet system, or any other known engagement system.

As shown in FIG. 3, a distal end 32 of the second member 14 engages a proximal end 34 of the stem component 26. In this embodiment, the distal end 32 of the second member 14 is threaded and fits inside a threaded bore of the proximal end 34 of the stem component 26. Alternatively, the distal end 32 of the second member 14 may have the threaded bore and the proximal end 34 of the stem component may be threaded. In other embodiments, other known means of connecting pieces may be used. For example, an expandable collet may be used. Alternatively, the connection means may be a retractable button/recess system, an undercut, a slotted l-shaped recess and rod system, an expandable collet system, or any other known engagement system.

The second member 14 also includes a proximal end 36 (FIG. 2). The proximal end 36 includes a knob 68 (FIG. 4). The knob 68 is coupled to the threaded distal end 32, such that as the knob 68 is rotated about the second member longitudinal axis 22, the threaded distal end 32 is threaded into the threaded bore proximal end 34 of the stem component 26.

Turning now to FIGS. 4-6, the washer system 16 will be described. The washer system 16 includes a first spiral washer 40 and a second spiral washer 42. The first spiral washer 40 is coupled to the drive mechanism 18 and includes a first spiral ramp 44 and the second spiral washer 42 is coupled to the second member 14 and the first spiral washer 40 and includes a second spiral ramp 46 (FIG. 5). The first spiral ramp 44 abuts the second spiral ramp 46. The washer system 16 has an overall starting height of h. As the first spiral ramp 44 is rotated relative to the second spiral ramp 46, the ramps engage one another, creating a gap 48 between the first spiral washer 40 and the second spiral washer 42. The gap 48 is of a distance D. As shown in FIGS. 5 and 6, the washers 40, 42 begin by being flush against one another. However, as the first spiral washer 40 is rotated, the spiral ramps 44, 46 are rotated enlarging the height of the two washers 40, 42. The distance D of the gap 48 remains the same. In FIG. 6, the overall height of the washer system 16 is now H, which is larger than h. This change in height is generated by the opposing spiral ramps 44, 46 engaging one another, creating a washer system 16 with a variable height.

As shown in FIG. 4, the first washer 40 includes a ratchet end 50 that opposes the spiral ramp 44. The first washer 40 is coupled to a ratchet washer 52. The ratchet washer 52 is connected to the handle 18. One side 54 of the ratchet washer 52 is ratcheted and mates with the ratchet end 50 of the first washer. As the handle 18 is turned, the ratchets on the ratchet washer 52 and first spiral washer 40 engage one another, causing the first spiral washer 40 to rotate. Because the second spiral washer 42 is fixed, the two spiral ramps 44, 46 engage and cause the first spiral washer 40 to become raised (by a height D) relative to the second spiral washer 42.

Referring still to FIG. 4 and also to FIG. 7, the second member 14 includes a sacrificial member 56, which in this case is a tensile rod or shear pin. The tensile rod 56 includes an intentional weak spot or breakage point 58. The breakage point 58 can only tolerate up to a specific tension. After that load (or tension) is reached, the breakage point 58 breaks, leaving two separate pieces 60, 62. As shown in FIG. 4, the tensile rod 56 links an upper part 64 of the second member 14 to a lower part 66 of the second member 14. As the handle 18 is turned, and the threaded distal end 32 of the second member 14 is threaded into the threaded bore of the proximal end 34 of the stem component 26, tension is created.

At the top of the upper part 64 of the second member 14, there is the knob 68, as described above. The knob 68 is turned to first thread the threaded end 32 of the second member 14 to the stem component 26.

The knob 68 is coupled to the first spiral washer 40 in any number of known methods. In one embodiment illustrated in FIG. 7 a, the knob 68 includes a pull rod 68 a having a shoulder 68 b. The shoulder 68 b is coupled to a counterbore 40 a in the first spiral washer 40, such that as the first spiral washer 40 rotates and moves upwards along the longitudinal axis 22, the knob 68 also moves upwards. In this embodiment, a bearing 69 is located between the shoulder 68 b and the counterbore 40 a. The bearing 69 illustrated is a rolling bearing and reduces the friction and torsional force felt by the pull rod 68 a (and thus the sacrificial member 56). By reducing the frictional and torsional forces felt by the sacrificial member 56, the linear force at which the sacrificial member 56 will break is kept more consistent. In other embodiments, other types of bearings may be used. In some embodiments, no bearing 69 may be used and the shoulder 68 b abuts the counterbore 40 a directly.

As stated above, as the first spiral washer 40 rotates, and moves up along the longitudinal axis 22, the knob 68 also moves upwards. Because the knob 68 and threaded end 32 are coupled to one another and the threaded end is fixed within the stem component, the movement of the knob 68 creates tension along the second member 14. Once the tension reaches a certain force (or load), the tensile rod 56 will break at the breakage point 58. A loud noise will be heard; also the knob 68 will become loose. The tensile rod 56 breaking is important because it signals to the user that enough force has been applied. In this embodiment, the tensile rod 56 is fixed to break at a predetermined force. In some embodiments, that force is between about 2000 lbf and about 2500 lbf, and preferably at about 2250 lbf. In some embodiments, the knob 68 may also be used to disengage the ratchet washer 52 from the ratchet end 50 of the first washer 40.

As shown in FIG. 7, the two halves 60, 62 of the tensile rod 56 are each fitted into slotted openings 70, 72, respectively, of the second member 14. A sleeve 74 fits around the tensile rod 56. As shown, the first half 60 and the second half 62 each include a rib 76, 78 respectively, that extends outwardly. The ribs 76, 78 each fit within a recess 80 a, 80 b of the sleeve 74. The ribs 76, 78 also engage an edge 82, 84 of the recesses 80 a, 80 b. Once the tensile rod 56 breaks, both the first and second halves 60, 62 remain contained within the sleeve 74. Even though the first and second halves 60, 62 are no longer connected directly to one another, rotation of one will cause the other to rotate. As the knob 68 is rotated, the slotted opening 70 rotates. This rotation causes the first half 60 of the tensile rod 56 to rotate. When the first half 60 rotates, it engages the edge 82 of the sleeve 74, causing the sleeve 74 to rotate. As the sleeve 74 rotates, the edge 84 engages the second half 62, causing the second half 62 to rotate. The second half 62 rotating engages the slotted opening 72, causing the lower portion 66 of the second member 14 to rotate, disengaging the threaded end 32 from the stem component 26. In another embodiment, the two halves 60, 62 of the tensile rod 56 are keyed together, such that even after the halves 60, 62 break, they are still coupled together. Then, when one half rotates, the other half also is forced to rotate.

In the above embodiment, the tensile rod 56 is held by the second member. However, in other embodiments, it may be held by the first member. Also, any known containment method may be used. Alternatively, the tensile rod 56 need not be contained.

In some embodiments, the sacrificial member 56 may not be a tensile rod, but could be a torsional member. Once loads are applied on a longitudinal axis, the torsional member feels rotational force (e.g., a torsional spring). The torsional spring could be weakened so as to break at a certain force. In other embodiments, the sacrificial member 56 could be designed to fail in both axial and torsional directions.

Generally, the assembly tool 10 may be made from stainless steel. In some embodiments, the tensile rod 56 are made from 440C stainless steel, while all other components are made from 17-4 stainless steel. In other embodiments, the assembly tool 10 may be made of plastic, with only the washer system 16 and the tensile rod 56 being made of stainless steel. In other embodiments, other metals may be used. The tensile rod 56 could be made from plastic, ceramic, or other polymer. In other embodiments, the sleeve 74 could also be made of plastic or other polymer. In other embodiments, the assembly tool 10 may entirely be made of a single composite material. In some embodiments, the tensile rod 56 could be a small fixture with a shear pin.

In some embodiments, the distal end 28 of the first member 12 could include dimples that would create impressions on the proximal end of the neck component 24. The impressions would serve as a direct correlation to the force applied to the modular construct, much like those produced by a Rockwell hardness test machine. The spherical dimples on 28 could be positioned (clocked), such that, 3-impressions would be created in each use, regardless of the instrument-to-implant orientation. The physical size of the dimples would be predetermined, based on the material hardness of the proximal body. Other dimension (other than spherical) dimples could also be used. Alternatively, a number other than three dimples may be used.

In some embodiments, there may be a biasing mechanism, such as a wave spring or other type of spring, used to keep the ratchet washer 52 engaged with the ratchet end 50 of the first washer 40. Other springs may be used in the device to cause the first washer 40 to spring back after being ratcheted. In some embodiments, the spring may be a constant force spring.

Turning now to FIG. 8, a flow chart describing the method of using the assembly tool 10 is shown. As shown, at step s100, the proximal component is inserted on to the stem component. Then the distal end of the second member is inserted into the opening of the stem component at step s102. When this is achieved, the distal end of the first member abuts the proximal end of the first component. At step s104, the knob is rotated threading the distal end of the second member into the stem component. The drive mechanism is then turned, causing the knob to move upward (step s106), as described above. Once a predetermined force is applied, the tensile rod breaks, indicating that the proper force has been applied (step s108). At step s110, the knob is rotated to disengage the threaded distal end from the stem component and the assembly tool is removed from the proximal and stem components (step s112).

Turning now to FIGS. 9 and 10, another embodiment of the present invention will be illustrated. In FIG. 9, a perspective view of an assembly tool 200 is shown. The assembly tool 200 includes a first member 202 and a second member 204. The first member 202 includes a distal end 206 (FIG. 10) that abuts a proximal end 208 of a neck component 210 of an implant 212. Alternatively, the connection means may be a retractable button/recess system, a slotted l-shaped recess and rod system, an undercut, an expandable collet system, or any other known engagement system.

A distal end 214 of the second member 204 engages a proximal end 216 of a stem component 218. In this embodiment, the distal end 214 of the second member 204 is threaded and fits inside a threaded bore of the proximal end 220 of the stem component 218. Alternatively, the distal end 214 of the second member 204 may have the threaded bore and the proximal end 216 of the stem component 218 may be threaded. In other embodiments, other known means of connecting pieces may be used. For example, an expandable collet may be used. Alternatively, the connection means may be a retractable button/recess system, an undercut, a slotted l-shaped recess and rod system, an expandable collet system, or any other known engagement system.

The second member 204 also includes a proximal end 221. The proximal end 221 includes a knob 222. The knob 222 is coupled to the threaded distal end 214, such that as the knob 222 is rotated about a second member longitudinal axis 224, the threaded distal end 214 is threaded into the threaded bore proximal end 220 of the stem component 218.

Turning now to FIG. 11, an exploded view of the assembly tool 200 is illustrated. As shown, the second member 204 is shown disassembled from the first member 202. The second member 204 includes a threaded cap 226. When assembled, the threaded cap 226 is threaded into a corresponding threaded bore 228 (FIG. 12).

As shown in FIGS. 11 and 11 a, a rod 229 having a hex end 229 a and a threaded end 229 b is shown. The rod 229 is threaded into a threaded recess 226 a of the cap 226. The male threads of the threaded end 229 b are made of stainless steel, such as 455 custom stainless steel and the cap 226 (including its female threads 226 a) are made of a Stainless Steel, such as Nitronic 60. 455 custom stainless steel is a hard material, while Nitronic 60 is comparably very soft. Thus, when the two are moved relative to one another, there is very little galling and the parts can be cycled a number of times before having to be replaced. The second member 204 also includes a tensile bar 230 that is sized and shaped to break at a predetermined force. This informs the user when the correct force has been reached. In some embodiments, that force is between about 2000 lbf and about 2500 lbf.

As shown in FIG. 13, the tensile bar 230 is held into place by a housing 232. The housing 232 includes an upper restraint 234 and a lower restraint 236. The upper restraint 234 is pivotally attached to the lower restraint 236 by extension arms 238 on the lower restraint and a pivot pins 239. The upper restraint 234 includes a t-shaped slot 240 that is shaped to engage the tensile bar 230. The opening of the t-shaped slot 240 faces one of the extension arms 238. The lower restraint 236 includes a t-shaped slot 242, with the opening facing perpendicular from the opening of the t-shaped slot 240 of the upper restraint 234. The lower restraint 236 also includes a spring-loaded lower section 241.

In use, the user would pull down on the spring-loaded lower section 241, and pivot the upper restraint 234 into an open position. The user then inserts the tensile bar 230 into the t-shaped slots. The upper restraint 234 is then pivoted back into alignment with the lower restraint 236 and the user releases the spring-loaded lower section 241. The opening of the t-shaped slot 240 of the upper restraint 234 is blocked by one of the extension arms and the opening of the t-shaped slot 242 of the lower restraint 236 is blocked by the released spring-loaded lower section 241.

During use, once the tensile bar 230 breaks, the t-shaped openings 240, 242 keep the respective halves of the tensile bar 230 in place along with the spring-loaded lower section 241 until the user is ready to disassemble the tool 200. Also, as described above in reference to assembly tool 10, the upper and lower restraints 234, 236 are keyed together, so that even after the tensile bar breaks, the upper and lower restraints 234, 236 still move together.

Returning now to FIGS. 9 and 10, the use of the assembly tool 200 will be described. As shown, the first member 202 includes a stationary handle 244 and a torque handle 246 is inserted onto the second member 204. To use, the assembly tool 200 is inserted into the proximal body 208 such that the distal end 206 of the first member abuts the proximal body 208. The distal end 214 of the second member is inserted into the threaded opening 220 of the stem 218 and the knob 222 of the second member 204 is rotated, causing the threaded distal end 214 of the second member 204 to threadingly engage the threaded opening 220 of the stem 218. The user then rotates the torque handle 246 while holding the handle 244 of the first member 202 stationary. During this use, the rod 229 is rotated relative to the cap 226 and the threaded end 229 a is moved relative to the cap 226, thereby moving the threaded distal end 214. The user continues to rotate until an audible sound is heard, indicating the breaking of the tensile bar 230. The user then disengages the tool 200 from the implant by rotating the knob 222 counterclockwise.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the present invention as defined by the appended claims. 

We claim:
 1. An assembly tool for assembly of a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty, the tool comprising: a first member operably associated with the first component; and a second member operably associated with the second component; wherein the second member includes a cap having a threaded recess and further includes a threaded rod adapted to engage the threaded recess so as to move the second member relative to the first member and the threaded rod is made of a harder metal than the threaded recess; wherein the second member includes a tensile bar comprising two halves fitted into slotted openings; wherein each half includes a rib section fitted into a recess in a sleeve and a curved section defining a breaking point located at a center point between the two halves; wherein the tensile bar is configured to break at the breaking point when a predetermined force is applied.
 2. The assembly tool of claim 1, wherein the threaded recess of the cap is made of a Nitinol and the threaded rod is made of a stainless steel.
 3. The assembly tool of claim 2, wherein the threaded recess of the cap is made of Nitronic 60 and the threaded rod is made of 455 custom stainless steel.
 4. The assembly tool of claim 1, wherein the predetermined force is between about 20001 bf and about 2500 lbf.
 5. The assembly tool of claim 1, wherein the second member includes a housing adapted to house the tensile bar.
 6. The assembly tool of claim 5, wherein the housing of the second member includes an upper restraint pivotally attached to the lower restraint.
 7. The assembly tool of claim 6, wherein the upper restraint includes a t-shaped slot having an opening adapted to receive the tensile bar.
 8. The assembly tool of claim 7, wherein the lower restraint includes a t-shaped slot having an opening perpendicular to the opening of the t-shaped slot of the upper restraint.
 9. An assembly tool for assembly of a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty, the tool comprising: a first member operably associated with the first component, the first member defining a first member longitudinal axis thereof; a second member operably associated with the second component, the second member including a tensile bar comprising two halves fitted into slotted openings; wherein each half includes a rib section fitted into a recess in a sleeve and a curved section defining a breaking point located at a center point between the two halves; wherein the tensile bar is configured to break at the breaking point when a predetermined force is applied; wherein the second member includes a housing configured to retain the tensile bar after the tensile bar breaks.
 10. The assembly tool of claim 9, wherein the predetermined force is between about 2000 lbf and about 25001 bf.
 11. The assembly tool of claim 9, wherein the housing of the second member includes an upper restraint pivotally attached to the lower restraint.
 12. The assembly tool of claim 11, wherein the upper restraint includes a t-shaped slot having an opening adapted to receive the tensile bar.
 13. The assembly tool of claim 11, wherein the lower restraint includes a t-shaped slot having an opening perpendicular to the opening of the t-shaped slot of the upper restraint.
 14. The assembly tool of claim 11, wherein the lower restraint includes a spring- loaded lower section adapted to contain the tensile bar in the lower restraint.
 15. The assembly tool of claim 9, wherein the second member includes a cap having a threaded recess and further includes a threaded rod adapted to engage the threaded recess so as to move the second member relative to the first member and the threaded rod is made of a harder metal than the threaded recess.
 16. The assembly tool of claim 15, wherein the threaded recess of the cap is made of a Nitinol and the threaded rod is made of a stainless steel.
 17. The assembly tool of claim 16, wherein the threaded recess of the cap is made of Nitronic 60 and the threaded rod is made of 455 custom stainless steel. 